University of Hawai'i astronomer John L. Tonry is a member of a research team that has won the $500,000 Gruber Cosmology Prize for the discovery that the expansion of the universe is accelerating.

Two teams of astronomers  one led by Brian Schmidt of Australian National University and the other by Saul Perlmutter of University of California, Berkeley  set out to look for evidence that the expansion of the universe was slowing down as a result of gravitational forces between the galaxies. Contrary to such expectation, both teams discovered that the expansion of the universe is apparently accelerating.

The force that is causing the universe to expand at an ever-increasing rate has been dubbed "dark energy," but its nature is still a mystery.

Tonry's contribution was the 1997 discovery of crucial supernovae explosions in distant galaxies using the Canada-France-Hawai'i Telescope on Mauna Kea.

"It was the CFHT data coupled with data from the Keck Observatory and the Hubble Space Telescope that were the key to identifying the accelerating universe," Tonry said in a news release issued today by the Institute for Astronomy at the University of Hawai'i.

IfA Director Rolf Kudritzki said in the release, "The university can be very proud of being associated with this prize. Dr. Tonry is an enormously accomplished researcher, and I am delighted that his contributions are being recognized in this way."

The Gruber Cosmology Prize honors a leading cosmologist, astronomer, astrophysicist or scientific philosopher for theoretical, analytical or conceptual discoveries leading to fundamental advances in the field. The teams will receive the prize Sept. 7 at a ceremony at the University of Cambridge.

For additional information about the prize, visit http://gruberprizes.org.